Spatial ecology of cheetahs on north-central Namibian farmlands L. L. Marker1,2, A. J. Dickman1,2 * , M. G. L. Mills3 †, R. M. Jeo1 ‡ & D. W. Macdonald2 1 Cheetah Conservation Fund, Otjiwarongo, Namibia 2 Wildlife Conservation Research Unit, Department of Zoology, Oxford, UK 3 South African National Parks, Endangered Wildlife Trust and Mammal Research Institute, University of Pretoria, Skukuza, South Africa * Current address: Nuffield Building, Institute of Zoology, Zoological Society of London, Regents Park, London NW1 4RY, UK. † Current address: Kgalagadi Cheetah Project, P. Bag X5890, Upington 8800, South Africa. ‡ Current address: The Nature Conservancy, 4245 North Fairfax Drive, Arlington, VA 22203 USA. Correspondence Laurie L. Marker, Cheetah Conservation Fund, PO Box 1755, Otjiwarongo, Namibia. Fax: 264 67 306247 Email: [email protected] Abstract Knowledge of a species' ranging behaviour is both fundamental to understanding its behavioural ecology and a prerequisite to planning its management. Few data exist on the spatial ecology of cheetahs Acinonyx jubatus outside protected areas, but such areas are particularly important to their conservation. Cheetahs on Namibian farmlands occupied exceptionally large home ranges, averaging 1651 km2 (±1594 km2), with no detectable effect of sex, social grouping or seasonality. Despite such large ranges, cheetahs tended to utilize intensively only a small fraction of that area: 50% of the fixes were located within an average of 13.9±5.3% of the home range. Ranges were not exclusive, overlapping on average by 15.8±17.0%, with male cheetahs showing more intra-sexual range overlap than did females. Coalitions of males appeared to select for a dense, prey-rich habitat, but this preference was not apparent for other social groupings. Conflict with humans is an important contributor to the species' decline, and these large, overlapping cheetah home ranges result in the movements of each individual cheetah encompassing many farms (21 based on the average home-range size). Consequently, many cheetahs may be exposed to a minority of farmers attempting to kill them, and also that many farmers may see the same cheetahs, thereby gaining an exaggerated impression of their abundance. Conservation priorities for cheetahs outside protected areas are the development of techniques for conflict resolution, as well as the maintenance and restoration of suitable habitat and promotion of land-management practices compatible with the continued existence of large carnivores. Introduction Although the creation and maintenance of a connected, representative protected-area network is important for both large carnivore persistence and biodiversity conservation (Margules & Pressey, 2000), the inadequate size of many protected areas means that management of surrounding lands may be equally important for conservation (Newmark, 1996). In Namibia, the majority of wildlife populations exist outside of protected areas (Barnard, 1998), with most of the country's ungulates occurring on commercial farmland (Richardson, 1998). This abundance of prey, coupled with the provision of artificial waterpoints and the widespread extirpation of large competitors, including lions Panthera leo and spotted hyaenas Crocuta crocuta, make commercial farmland a favourable refuge for cheetahs Acinonyx jubatus (Marker-Kraus et al., 1996). Approximately 90% of Namibia's estimated 3000 cheetahs are found on 275 000 km2 of farmland in the north-central region of the country (Morsbach, 1987; Marker-Kraus & Kraus, 1990). This distribution has caused conflict with farmers, who perceive cheetahs as a significant threat to both livestock and ranched wildlife (Marker, Mills & Macdonald, 2003c). This conflict led to large numbers of cheetahs being killed or taken into captivity, with an estimated halving of the population size during the 1980s (Morsbach, 1987), and also meant that farmers who captured cheetahs and reported them to the Cheetah Conservation Fund (CCF) were often unwilling to have animals re-released onto their land. Therefore, cheetahs were often moved substantial distances, which could have a marked effect on their spatial ecology in this system. Although conservation efforts seem to have reduced this conflict (Marker et al., 2003c), understanding cheetah ecology in this landscape is crucial for developing effective management strategies. Our goal was to describe cheetah ranging behaviour on Namibian farmlands. Inter- sexual differences in spatial ecology are widely reported (Wilson, 1975; Caro, 1994), and so we examined home-range size in relation to sex, social group composition, age and season. Various aspects of cheetah spatial ecology have been documented previously (Caro, 1994; Durant, 1998; Broomhall, Mills & du Toit, 2003), but the only detailed, long-term study to date has been conducted in Serengeti National Park. This study provides the first long-term information regarding cheetah ranging behaviour outside of protected areas. Study area Radio tracking was conducted within an 18 000 km2 area in north-central Namibia. The study area primarily consisted of commercial farmland, but also encompassed the Waterberg Plateau (a 48 × 16 km protected area), communal farmland and several fenced game-farms (Fig. 1). The area received an average of 472 mm rainfall annually, with 93% rain falling in the wet season (15th September to 14th April) and 7% in the dry season (15th April to 14th September). The area was generally flat, with slow rainfall run-off, no permanent rivers and numerous man-made semi-permanent water reservoirs. Figure 1 Radio tracking study area, in the north-central Namibian commercial farmland, used to track radio collared cheetahs Acinonyx jubatus between 1993 and 2000. Land use in the area was primarily commercial cattle and wildlife farming, with a low human population density, averaging 2.3 people km2 (CIA, 2003). The majority of commercial farms were individually owned and ranged in size from 50 to 200 km2, with a mean of 80 km2 (Marker-Kraus et al., 1996). The area was situated in the Thornbush Savannah vegetation zone (Geiss, 1971), with Acacia, Dichrostachys, Grewia, Terminalia and Boscia being the dominant woody plant genera. Methods Between 1993 and 2000, radio collars were fitted onto 41 wild caught cheetahs on Namibian commercial farmland. Cheetahs were captured opportunistically, mainly by local farmers but also by CCF researchers, using box traps (see Marker et al., 2003a for details). Cheetahs were classified as being in one of the following social groupings: male coalition, single male or female (with or without cubs) for analyses. If one cheetah was caught, further traps were placed beside it until there was confidence, from lack of spoor or other signs of other cheetahs nearby, that the animal was a singleton or that all members of the social group had been captured. Cheetahs were examined either at the capture site or at CCF headquarters. Immobilization was achieved using Telazol® (tiletamine-HCl and zolazepam-HCl; Warner Lambert, Ann Arbor, MI, USA), administered at 4 mg/kg intramuscularly. Cheetahs were fitted with a neoprene radio tracking collar with an external antenna (Advanced Telemetry Systems, Isanti, MN, USA), which had a life expectancy of >36 months. Radio collars weighed 280 g, equivalent to 0.56% of body mass for a 50 kg male and 0.76% for a 37 kg female, well below the 3% limit recommended by Kenward (2001). We found no evidence of collars affecting survival or behaviour, and the same design has been used previously without evidence of significant adverse effects (Laurenson & Caro, 1994). Age classification was based on experience with captive cheetahs and upon information from previous studies (Burney, 1980; Caro, 1994) and derived from weight, body measurements, tooth condition, gum recession, pelage condition, reproductive condition and social groupings of animals (Marker & Dickman, 2003). We categorized adult cheetahs at the time of collaring as: newly independent (>18– 30 months), young adults (>30–48 months), prime adults (>48–96 months) and old adults (>96–144 months). None of the cheetahs radio collared was estimated to be over 144 months old. To give confidence to the above process, a cementum ageing model, as described in Matson (1981), was used on a subsample of individuals recovered after death, as well as from known-age animals, which revealed a good correlation between estimated and actual ages (Matson's Laboratory, LLC, Milltown, MT, USA; Marker et al., 2003a). Full details of the criteria used to assign cheetahs to age classes are provided in Marker & Dickman (2003). Depending on the landowner who had caught the animal, cheetahs were either released at the capture site, or on other farms where ranchers had given permission. The distance from capture to release site ranged from 0 to 600 km (Table 1). Only one cheetah per social group was radio collared, and cheetahs were released in the grouping with which they had been captured. Young, dependent cheetahs were only released if they were captured with their mothers, and animals were not collared unless they were fully grown. Wherever possible, radio collars were retrieved at the end of the project, but this was not always feasible due to the opportunistic nature of cheetah capture, and occurred in 63% of the cases. Table 1 Information regarding all cheetahs Acinonyx jubatus radio-tracked on the Namibian farmlands during this study Social group categories are as follows: SM, single male; CM, coalition male; F, female. Cheetahs were assigned to one of the following age groups at time of radio collaring: 1=newly independent (>18–30 months), 2=young adult (>30–48 months), 3=prime adult (>48–96 months) and 4=old adult (>96–144 months). None of the radio collared cheetahs was estimated to be >144 months old. MCP, minimum convex polygon; HRS, home-range size. Radio tracking Following release, radio-collared cheetahs were tracked from a Cessna 172 aeroplane, utilizing a dual antenna procedure, with the animal's location determined using a portable global positioning system. Between May 1993 and May 1996, aerial tracking was conducted twice a week, while from June 1996 to December 2000 it was conducted once a week. Home-range area and overlap calculations Data were plotted and analysed using ArcView GIS (version 3.2, ESRI, Redlands, CA, USA) and the Animal Movement extension (Hooge, Eichenlaub & Soloman, 1999). Latitude and longitude recordings were used to calculate 95% minimum convex polygon (MCP) home ranges (White & Garrott, 1990), as well as 95 and 50% adaptive kernel home-range estimates (Worton, 1989; Seaman et al., 1999). Four estimates of home-range size were calculated: (1) overall (the entire length of time a cheetah was tracked); (2) annual (based on 12-month periods from the time of collaring); (3) dry season; (4) wet season home-range size. Analysis was restricted to cheetahs with enough fixes to reach an asymptotic level, as determined using Ranges V (Kenward & Hodder, 1996), and was set at ≥30 fixes within a year for overall and annual home range and ≥15 fixes within a season for seasonal home range. When the effect of age on range size was being investigated, analyses were restricted to the first year after collaring, to improve the likelihood that cheetahs remained in the age group in which they had originally been classified. Core home-range size was defined as the 50% probability kernel, and was determined for all cheetahs whose overall home range had been calculated. The degree of home- range overlap between cheetahs tracked concomitantly was calculated for each year of the study using the dynamitic interaction analysis as described in Ranges V (Kenward & Hodder, 1996). This analysis uses Jacob's Index (Jacobs, 1974), which compares the observed and possible distances between each range and provides a single index for each pair of animals. Habitat selection The habitat type in which each radio-telemetry fix occurred was visually classified from the air, and categorized in terms of bush density, namely sparse (<30% canopy), medium (30–75% canopy) and thick bush (>75% canopy). We also flew stratified random transects 20 km apart over the entire study area, and every 5 km, bush density was visually classified as above. This allowed estimation of the relative proportions of each habitat type available to cheetahs in the study area, providing a baseline for assessing habitat selection. Prey density in different habitat types was calculated by driving strip counts across 70 km2 of the study area, while the availability of different habitat types across that area was assessed using aerial photographs and ground observations. A minimum of three counts, over a standardized 50 km route, was conducted each month. The program DISTANCE (Thomas et al., 1998) was used to estimate prey density, and the strip was classified by habitat type, as above. The relative utilization of habitat types by prey species was examined alongside cheetah habitat selection, to investigate whether cheetahs' favoured habitat that was selected for by ungulates. Data analysis Analyses were conducted using the statistical package SPSS version 12.0.1 (SPSS Inc. Chicago, IL, USA). The statistical tests used depended on the distribution of the data and included χ2, t-test, z-test, Kruskal–Wallis (KW) χ2, analysis of variance and Spearman's and Pearson's correlations, with P<0.05 considered to be significant. Results Forty-one cheetahs (26 males, 15 females) were radio-tracked between April 1993 and December 2000 (Table 1). Cheetahs were located on 87.4% (±12.6) of the flights, during which they were searched, and overall, annual and seasonal home ranges were determined from a mean of 68.34 (±68.14) fixes per cheetah, and 7.4 (±2.8) days between fixes. Because cheetahs were opportunistically caught, we examined their ages in order to reveal potential biases in sampling before comparing social groupings and sexes (Table 1). There was no significant difference between sexes regarding age category at collaring (z=−0.562, P=0.602); however, there was between social groupings (KW χ2=6.549, P=0.038), as single males were significantly older at the time of collaring (z=−2.73, P=0.006) when compared with other groupings. There were no significant differences between the mean number of fixes (F=0.087, P=0.917), percentage of flights on which they were located (F=1.070, P=0.353) or the number of months tracked (KW χ2=0.472, P=0.790). Overall home-range size Twenty-seven cheetahs yielded sufficient fixes to estimate overall home-range size, which revealed a mean overall range size of 1651.1 km2 (±1594.2 km2) and a median overall range size of 1146.5 km2 (Table 1). Estimates of overall home-range size produced using the 95% kernel method did not vary significantly from those using the 95% MCP, for any of the social groupings (single males: z=−0.115, P=0.908; coalition males: z=−0.831, P=406; females: z=−0.315, P=0.753). Therefore, the 95% kernel method was used for further estimates of home-range size. No statistically significant differences were detected in home-range size between sexes (t=−1.081, P=0.290) or social groupings (F=0.580, P=0.586). For all social groupings, the overall home-range sizes estimated here were significantly larger than those reported elsewhere (single males: t=−5.15, P=0.036; coalition males: t=−18.9, P=0.001; females: t=−15.8, P<0.001: Table 2). Despite the general trend for vast ranges, some individuals still managed to exist within relatively small areas. Three single males, with a mean of 46 months of age, each occupied overall ranges of <300 km2, which might be considered to be large for cheetahs elsewhere, but tiny compared with the averages found here. In addition, ranges shifted between years (Fig. 2), and some home ranges were shown to increase when a male coalition was reduced to a single male (Fig. 3). Table 2 Estimates of cheetah Acinonyx jubatus home ranges sizes, and methods of estimation, reported in this study and elsewhere in Africa Figures in parentheses indicate sample size, that is the number of single males, single females or coalitions of males radio collared. MCP, minimum convex polygon; HRS, home-range size. *Male ranges given for the Serengeti refer to resident and non-resident males rather than coalitions and singletons respectively. Figure 2 Home range of a male coalition group (cheetah ID# 974) during the dry season of 1995 (a) and 1996 (b) showing a major shift in home range between the 2 years. Figure 3 One of the largest home ranges during the 10-year study was of a single male cheetah Acinonyx jubatus (ID# 985), which, after losing his coalition member, continued to shift his movement patterns and increase his home-range size. Annual home-range size Annual home-range sizes could be calculated for 23 cheetahs (Table 3). The mean annual range sizes did not differ significantly from the overall home-range size for any of the social groupings, and did not vary significantly between age groups, sexes or social groupings. Table 3 Mean annual home-range size (HRS) (estimated using the 95% kernel method) for all cheetahs Acinonyx jubatus radio-tracked during the study for at least 12 months, split by sex and social group by age Seasonal home-range size Neither wet nor dry season home-range size differed significantly between sexes, social groupings or age groups (Table 1). There was no significant difference between the size of wet and dry season home ranges for any of the social groupings: their boundaries shifted over time but did not differ significantly in terms of overall size. Core home-range size No significant seasonal variation was observed regarding core home-range area for any of the social groupings. Core areas comprised a significantly smaller percentage of single males' overall home range in the wet season (11.3±5.0%) than in the dry season (14.5±2.9%; z=−2.13, P=0.034), but no significant difference was found for the other social groupings. The sizes of coalition males' core home ranges were significantly smaller than those of females (z=−2.19, P=0.028), but there were no detectable differences between other social groupings. Core areas comprised on average 13.9±5.3% of the home- range size, with no significant difference between social groupings.
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